This video illustrates the complexity of Earth’s magnetic environment, from the radiation belts encircling Earth to the magnetic field lines, depicted as blue ribbons, extending far out into space. During a drop-out, ultra-relativistic electrons stream down along powerful electromagnetic waves, as if they are raining into the atmosphere.

Credits: NASA Goddard/Joy Ng/Martin Rother/GFZ-Potsdam

Our planet is nestled in the center of two doughnut-shaped regions of powerful, dynamic radiation: the Van Allen belts, where high-energy particles are trapped by Earth’s magnetic field. Depending on incoming radiation from the sun, they can gain energetic particles. On the other hand, the belts can lose energized particles too.

We are familiar with rapid changes in weather, and the radiation belts can experience these too – particles can be depleted by a thousand-fold in mere hours. These dramatic loss events are called drop-outs, and they can happen when intense bouts of solar radiation disturb Earth’s magnetic environment. There have been many theories on how this happens, but scientists have not had the data to pinpoint which one is correct.

However, on Jan. 17, 2013, NASA's Van Allen Probes were in just the right position to watch a drop-out in progress and resolve a long-standing question as to how the lower region of the belts close to Earth loses high-energy electrons – known as ultra-relativistic electrons for their near-light speeds. During a drop-out, a certain class of powerful electromagnetic waves in the radiation belts can scatter ultra-relativistic electrons. The electrons stream down along these waves, as if they are raining into the atmosphere. A team led by Yuri Shprits of University of California in Los Angeles published a paper summarizing these findings in Nature Communications on Sept. 28, 2016.

Such information helps illustrate the complexity of Earth's magnetic surroundings. Understanding changes within the belts is crucial for protecting the satellites and astronauts travelling through this sometimes harsh space environment.